Bulk acoustic wave resonator and filter including the same

ABSTRACT

A bulk acoustic wave resonator includes a substrate, a first electrode and a second electrode disposed on the substrate, and a piezoelectric layer disposed between the first electrode and the second electrode. At least one of the first electrode and the second electrode includes an alloy of molybdenum and tantalum.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims benefit of priorities to Korean PatentApplications No. 10-2015-0085236 filed on Jun. 16, 2015 and No.10-2016-0074741 filed on Jun. 15, 2016 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND

1. Field

The present disclosure relates to a bulk acoustic wave resonator and afilter including the same.

2. Description of Related Art

In accordance with the recent rapid development of mobile communicationsdevices, chemical and biological devices, and the like, demand forsmall, lightweight filters, oscillators, resonant elements, acousticresonant mass sensors, and the like has increased.

As a means for implementing such small, lightweight filters,oscillators, resonant elements, acoustic resonant mass sensors, and thelike, a bulk acoustic resonator has commonly been used. Such a bulkacoustic resonator has positive attributes in that it may bemass-produced at a minimal cost and may be subminiaturized. Further, thebulk acoustic resonator has advantages in that it may implement a highquality Q factor, a main property of a filter; may be used in amicro-frequency band; and may particularly be implemented in bands ofpersonal communication system (PCS) and digital cordless system (DCS).

Generally, the bulk acoustic resonator has a structure including aresonating part implemented by sequentially laminating a lowerelectrode, a piezoelectric layer, and an upper electrode on a substrate.When an electric field is maintained in the piezoelectric layer byapplying electrical energy to the lower and upper electrodes, theelectric field causes a piezoelectric phenomenon in the piezoelectriclayer, thereby causing the resonating part to be vibrated in apredetermined direction. As a result, an acoustic wave is generated inthe same direction as the vibration direction of the resonating part,thereby causing resonance.

SUMMARY

An exemplary embodiment in the present disclosure may provide a bulkacoustic wave resonator in which reliability may be secured bypreventing oxidation of electrodes and crystal orientation of apiezoelectric layer formed on an electrode may be improved.

According to an exemplary embodiment in the present disclosure, at leastone of a plurality of electrodes of a bulk acoustic wave resonator maybe formed using an alloy of molybdenum and tantalum.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features and other advantages of thepresent disclosure will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional view illustrating a bulk acoustic waveresonator according to an embodiment;

FIG. 2 is Pourbaix diagrams of molybdenum (Mo);

FIG. 3 illustrates a phase diagram for a molybdenum (Mo)-tantalum (Ta)alloy;

FIG. 4 illustrates a Raman shift for each type of molybdenum (Mo) alloy;

FIG. 5 illustrates a change in sheet resistance of a molybdenum(Mo)-tantalum (Ta) alloy according to an embodiment;

FIGS. 6A and 6B are diagrams illustrating crystal orientation ofaluminum nitride (AlN) at a molybdenum (Mo)-tantalum (Ta) alloy phaseaccording to an embodiment; and

FIGS. 7 and 8 are schematic circuit diagrams of filters according toexemplary embodiments.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described asfollows with reference to the attached drawings.

The present disclosure may, however, be exemplified in many differentforms and should not be construed as being limited to the specificembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the disclosure to those skilled in the art.

Throughout the specification, it will be understood that when anelement, such as a layer, region or wafer (substrate), is referred to asbeing “on,” “connected to,” or “coupled to” another element, it can bedirectly “on,” “connected to,” or “coupled to” the other element orother elements intervening therebetween may be present. In contrast,when an element is referred to as being “directly on,” “directlyconnected to,” or “directly coupled to” another element, there may be noelements or layers intervening therebetween. Like numerals refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be apparent that though the terms first, second, third, etc. maybe used herein to describe various members, components, regions, layersand/or sections, these members, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one member, component, region, layer or section fromanother region, layer or section. Thus, a first member, component,region, layer or section discussed below could be termed a secondmember, component, region, layer or section without departing from theteachings of the embodiments.

Spatially relative terms, such as “above,” “upper,” “below,” and “lower”and the like, may be used herein for ease of description to describe oneelement's relationship to another element(s) as shown in the figures. Itwill be understood that the spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. For example, if thedevice in the figures is turned over, elements described as “above,” or“upper” other elements would then be oriented “below,” or “lower” theother elements or features. Thus, the term “above” can encompass boththe above and below orientations depending on a particular direction ofthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may be interpreted accordingly.

The terminology used herein describes particular embodiments only, andthe present disclosure is not limited thereby. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises,” and/or “comprising”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, members, elements, and/or groupsthereof, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, members, elements, and/orgroups thereof.

Hereinafter, embodiments of the present disclosure will be describedwith reference to schematic views illustrating embodiments of thepresent disclosure. In the drawings, for example, due to manufacturingtechniques and/or tolerances, modifications of the shape shown may beestimated. Thus, embodiments of the present disclosure should not beconstrued as being limited to the particular shapes of regions shownherein, for example, to include a change in shape results inmanufacturing. The following embodiments may also be constituted by oneor a combination thereof.

The contents of the present disclosure described below may have avariety of configurations and propose only a required configurationherein, but are not limited thereto.

FIG. 1 is a cross-sectional view illustrating a bulk acoustic waveresonator according to an embodiment.

Referring to FIG. 1, a bulk acoustic wave resonator 100 according to anembodiment is a film bulk acoustic resonator (hereinafter, referred toas “FBAR”) and includes a substrate 110, an insulating layer 120, an aircavity 112, and a resonating part 135.

The substrate 110 is configured of a silicon substrate, and theinsulating layer 120 is disposed on an upper surface of the substrate110 to electrically insulate the resonating part 135 from the substrate110.

The insulating layer 120 is formed by depositing at least one of SiO₂,Si₃N₄, Al₂O₂, and AlN on the substrate 110 by one of a chemical vapordeposition method, an RF magnetron sputtering method, and an evaporationmethod.

The air cavity 112 is disposed above the substrate 110. The air cavity112 is disposed below the resonating part 135 in such a manner that theresonating part 135 may be vibrated in a predetermined direction. Theair cavity 112 is formed by processes of forming a sacrificial aircavity layer pattern on the insulating layer 120, then forming amembrane 130 on the sacrificial air cavity layer pattern, and etchingand removing the sacrificial air cavity layer pattern. The membrane 130may serve as an oxidation protection layer or serve as a protectionlayer protecting the substrate 110. Although not illustrated in FIG. 1,a seed layer formed using aluminum nitride (AlN) is disposed on themembrane 130. In detail, the seed layer is disposed between the membrane130 and a first electrode 140.

Although not illustrated in FIG. 1, an etch-stop layer may be furtherformed on the insulating layer 120. The etch-stop layer may serve toprotect the substrate 110 and the insulating layer 120 from an etchingprocess for removing a sacrificial layer pattern and may serve as a basenecessary to deposit various other layers on the etch-stop layer.

The resonating part 135 may include the first electrode 140, apiezoelectric layer 150, and a second electrode 160 which aresequentially laminated.

The first electrode 140 is provided in a form extended from a positionon an upper portion of the insulating layer 120 to a position of themembrane 130 disposed on the air cavity 112, to cover a portion of themembrane 130. The piezoelectric layer 150 is formed on a portion of thefirst electrode 140 disposed on the air cavity 112. The second electrode160 is formed to be extended from a position on another upper portion ofthe insulating layer 120 to a position of the piezoelectric layer 150disposed above the air cavity 112, to be disposed on the piezoelectriclayer 150. A common region in which the first electrode 140, thepiezoelectric layer 150, and the second electrode 160 overlap each otherin a vertical direction is disposed above the air cavity 112.

The piezoelectric layer 150, a part in which a piezoelectric effect isgenerated by converting electrical energy into mechanical energy of anacoustic wave type, is formed of one of aluminum nitride (AlN), zincoxide (ZnO), and lead zirconium titanium oxide (PZT; PbZrTiO). Thepiezoelectric layer 150 may further include a rare earth metal. As anexample, the rare earth metal may include at least one of Sc, Er, Y, andLa.

The resonating part 135 may be classified as having an active region andnon-active regions. The active region of the resonating part 135 is aregion vibrated in a predetermined direction by a piezoelectricphenomenon generated in the piezoelectric layer 150 when electricalenergy such as radio frequency (RF) signals is applied to the first andsecond electrodes 140 and 160, and corresponds to a region in which thefirst electrode 140, the piezoelectric layer 150, and the secondelectrode 160 overlap each other in a vertical direction above the aircavity 112. The non-active regions of the resonating part 135 areregions which are not resonated by the piezoelectric phenomenon even inthe case that electrical energy is applied to the first and secondelectrodes 140 and 160, and correspond to outer regions of the activeregion.

The resonating part 135 outputs a radio frequency signal having aspecific frequency using a piezoelectric phenomenon, and in detail,outputs a radio frequency signal having a resonance frequencycorresponding to a degree of vibration based on the piezoelectricphenomenon of the piezoelectric layer 150.

A protection layer 170 is disposed on the second electrode 160 of theresonating part 135 to prevent the second electrode 160 from beingexposed externally and oxidized, and an electrode pad 180 to allow anelectrical signal to be applied is formed on portions of the firstelectrode 140 and the second electrode 160 which are exposed externally.

FIG. 2 is Pourbaix diagrams of molybdenum (Mo).

The first and second electrodes 140 and 160 are generally formed of oneof gold (Au), titanium (Ti), tantalum (Ta), molybdenum (Mo), ruthenium(Ru), platinum (Pt), tungsten (W), aluminum (Al), iridium (Ir), andnickel (Ni). In detail, in order to increase crystal orientation of thepiezoelectric layer 150, molybdenum (Mo) is used.

However, referring to FIG. 2, molybdenum (Mo) may have problems that ittends to be dissolved at a pH of 4 to 7 and tends to be oxidized inother pH regions. In order to solve the above-mentioned problems,molybdenum (Mo) is hermetically sealed to be passivation-treated.

However, even in the case that molybdenum (Mo) is passivation-treated asdescribed above, when molybdenum (Mo) is exposed to moisture at the timeof performing a moisture treatment process, it will be apprehended thatmolybdenum (Mo) is oxidized. Since oxidized molybdenum (Mo) also hasrelatively high solubility, it may cause a reliability problem. Forexample, in order to connect the first electrode 140 to an externalcircuit, when a specific region of the first electrode 140 is exposed bya trench and is then connected to the electrode pad 180 of FIG. 1,connection and contact defects may be caused.

In order to solve the above-mentioned problems, in a case in which thefirst and second electrodes 140 and 160 are formed of metals other thanmolybdenum (Mo), problems that high specific resistance is involved andorientation is decreased at the time of depositing the piezoelectriclayer 150 may occur.

According to an embodiment, the first and second electrodes 140 and 160include a molybdenum (Mo) alloy. As an example, one of the first andsecond electrodes 140 and 160 is formed using a molybdenum (Mo)-tantalum(Ta) alloy.

According to an embodiment, one of the first and second electrodes 140and 160 is formed of a molybdenum (Mo)-tantalum (Ta) alloy, to implementrelatively low specific resistance characteristics of the first andsecond electrodes 140 and 160 and easily perform an etching process.Further, relatively high crystal orientation of the piezoelectric layer150 may be obtained.

Further, in the molybdenum (Mo)-tantalum (Ta) alloy, the content oftantalum (Ta) is 0.1 to 50 atm %, in detail, 0.1 to 30 atm %.

FIG. 3 illustrates a phase diagram for a molybdenum (Mo)-tantalum (Ta)alloy.

Referring to FIG. 3, the molybdenum (Mo)-tantalum (Ta) is a homogeneoussolid solution formed in a single phase when a temperature is decreasedin a liquid phase, and has the same atomic structure such as abody-centered cubic (BCC). Thus, for example, when the first electrode140 is formed using the molybdenum (Mo)-tantalum (Ta) alloy, crystalorientation characteristics of the piezoelectric layer formed on thefirst electrode 140 are improved.

With reference to FIG. 3, when the content of Ta in themolybdenum(Mo)-tantalum(Ta) alloy is 30 atm % or less, a meltingtemperature thereof is substantially constant, while in a case in whichthe content of Ta in the molybdenum(Mo)-tantalum(Ta) alloy exceeds 30atm %, a melting temperature thereof is rapidly increased to cause aproblem in forming the first and second electrodes 140 and 160 using themolybdenum(Mo)-tantalum(Ta) alloy.

Thus, according to an embodiment in the present disclosure, the firstand second electrodes 140 and 160 may be easily formed using themolybdenum(Mo)-tantalum(Ta) alloy including 0.1 to 30 atm % of Ta.

FIG. 4 illustrates a Raman shift for each type of molybdenum (Mo) alloy.In detail, FIG. 4 illustrates a result of a Raman shift after an 8585reliability test (a test under a temperature of 85° C. and humidity of85%) is performed for a sample of the molybdenum (Mo) alloy. In FIG. 4,the content of niobium (Nb) in a molybdenum(Mo)-niobium (Nb) alloy is4.2 to 6.2 atm %, and the content of Ta in the molybdenum(Mo)-tantalum(Ta) alloy is 3.3 to 3.8 atm %.

In FIG. 4, a Raman shift for molybdenum oxide (MoO₂, MoO₃) refers to areference peak. It can be appreciated that in a Raman shift ofmolybdenum (Mo_1) in which a 8585 reliability test is not performed, apeak similar to that of a graph of molybdenum oxide (MoO₂, MoO₃) is notdetected, but in a Raman shift of molybdenum (Mo_2) in which the 8585reliability test is performed, a peak similar to that of the graph ofmolybdenum oxide (MoO₂, MoO₃) is detected and oxidized. It can also beseen that a result similar thereto is obtained in the Mo—Nb alloy.

However, a Raman shift for a Mo—Ta alloy is maintained at asubstantially constant value, from which it can be seen that in the caseof the Mo—Ta alloy, oxidization only slightly occurs.

Thus, according to an embodiment, at least one of the first and secondelectrodes 140 and 160 is formed of the molybdenum (Mo)-tantalum (Ta)alloy. Thereby, the oxidation problem which is caused when puremolybdenum (Mo) is used is solved, thereby increasing environmentalreliability.

FIG. 5 illustrates a change in sheet resistance of amolybdenum(Mo)-tantalum(Ta) alloy according to an embodiment. In detail,FIG. 5 illustrates a result of a change in sheet resistance after an8585 reliability test (a test under a temperature of 85° C. and humidityof 85%) was performed on a sample of the molybdenum (Mo) alloy.

It can be seen from the 8585 reliability test that sheet resistance ofpure molybdenum (Mo) was sharply increased after two days after thedeposition and was outside of a measurement range, but the molybdenum(Mo)-tantalum (Ta) alloy had a rate of change (%) of sheet resistanceless than 50%, even after three days and sheet resistance thereof wasnot significantly changed even in a high temperature and humidityenvironment.

The following Table 1 is provided to illustrate etching characteristicsof a molybdenum (Mo) alloy according to an embodiment.

As described above, the air cavity 112 is formed by etching thesacrificial air cavity layer pattern. An etching process of thesacrificial air cavity layer pattern is performed using xenon fluoride(XeF₂). Here, the etching process is performed after one of the firstand second electrodes 140 and 160 with reference to FIG. 1 is formed. Ina case in which the electrode is unnecessarily etched or corrodes by theetching process, a problem in which reliable resonance characteristicsof the bulk acoustic wave resonator is not secured may occur.

According to an embodiment, the electrode is formed of the molybdenum(Mo)-tantalum (Ta) alloy to secure robust characteristics for theetching material.

Table 1 is a table illustrating etching characteristics of puremolybdenum (Mo) and a molybdenum (Mo)-tantalum (Ta) alloy for xenonfluoride (XeF₂). In order to perform a test of Table 1, after puremolybdenum (Mo) and a molybdenum (Mo)-tantalum (Ta) alloy weredeposited, a portion of a deposition layer was removed by a circlehaving a diameter of 30 μm and a predetermined deposition thickness, andan inner portion of the circle was etched with xenon fluoride (XeF₂).

TABLE 1 Diameter Thickness of of Amount of Deposition Circle EtchingMolybdenum (Mo) 224 nm 68.99 μm 38.99 μm Molybdenum 136 nm 51.13 μm21.13 μm (Mo)-Tantalum (Ta) Alloy

As can be seen from Table 1, a diameter of a circle of pure molybdenum(Mo) is increased from 30 μm to 68.99 μm, such that 38.99 μm is etched,while a diameter of a circle of a molybdenum (Mo)-tantalum (Ta) alloy isincreased from 30 μm to 51.13 μm, such that 21.13 μm is etched. It isseen that the molybdenum (Mo)-tantalum (Ta) alloy was etched less thanmolybdenum (Mo) by about 50%, and it is seen that when a thickness ofdeposition is considered, the molybdenum (Mo)-tantalum (Ta) alloy wasetched less than molybdenum (Mo) by about 25%.

In detail, even in a case in which the molybdenum (Mo)-tantalum (Ta)alloy is inevitably exposed externally under the etching environment ofthe sacrificial air cavity layer pattern, reliability may be secured dueto robust characteristics for xenon fluoride (XeF₂).

FIGS. 6A and 6B are diagrams illustrating crystal orientation ofaluminum nitride (AlN) in a molybdenum (Mo)-tantalum(Ta) alloy phaseaccording to an embodiment.

FIG. 6A illustrates a rocking curve in a case in which aluminum nitride(AlN) is deposited on molybdenum (Mo) and molybdenum (Mo)-tantalum(Ta)alloy phases, and FIG. 6B illustrates full width at half maximum (FWHM)in a case in which aluminum nitride (AlN) is deposited on molybdenum(Mo) and molybdenum (Mo)-tantalum(Ta) alloy phases. In the case thataluminum nitride (AlN) is deposited on molybdenum (Mo) and molybdenum(Mo)-tantalum(Ta) alloy phases, the molybdenum (Mo) alloy and themolybdenum (Mo)-tantalum(Ta) alloy were formed to respectively have athickness of 0.23 μm, and the aluminum nitride (AlN) was formed to havea thickness of 0.9 μm.

Referring to FIG. 6A, it is seen that aluminum nitride (AlN) is grown ina c-axis orientation ([0002] direction) on all of molybdenum(Mo)-tantalum (Ta) alloy and pure molybdenum (Mo) phases. However,referring to FIG. 6B, it is seen that a FWHM of aluminum nitride (AlN)is 1.6308° on pure Mo, while is 1.5986° on the Mo—Ta alloy. Thus, it canbe appreciated that the FWHM of aluminum nitride (AlN) exhibits asmaller value under the molybdenum (Mo)-tantalum (Ta) alloy rather thanpure molybdenum (Mo). For example, a relatively high degree of crystalorientation may be obtained in a case in which the piezoelectric layer150 formed of aluminum nitride (AlN) is formed on the Mo—Ta alloy phase,rather than forming a piezoelectric layer formed of AlN on the pure Mophase.

Table 2 is a table illustrating values measured by manufacturing aresonator of the embodiment of the present disclosure in which anelectrode is formed using a Mo—Ta alloy and a resonator of a comparativeexample in which an electrode is formed of Mo. In the embodiment of thepresent disclosure, the first electrode 140 and the second electrode 160of FIG. 1 were manufactured using a Mo—Ta alloy to have thicknesses of0.23 μm and 0.24 μm, respectively. In the comparative example, the firstelectrode 140 and the second electrode 160 of FIG. 1 were manufacturedusing Mo to have thicknesses of 0.23 μm and 0.24 μm, respectively.

TABLE 2 Leakage Leakage Current Density (nA) (A/cm²) Fs (MHz) Fp (MHz)Kt² Embodiment 0.000 0 2615.92 2687.95 6.44 Comparative 0.168 1.675 *10⁻⁶ 2621.19 2687.39 5.93 Example

In Table 2, a level of leakage current was measured by applying avoltage of 20V to a resonator. In the case of the embodiment, a leakagecurrent was not detected, while in the case of the comparative example,the leakage current of 0.168 nA was detected. A leakage densitycorresponding to a level of leakage current detected per area of aresonator was calculated as 1.675*10⁻⁶. Thus, it can be appreciated thata relatively high degree of crystal orientation may be obtained in thecase that the piezoelectric layer 150 formed of aluminum nitride (AlN)is formed on the Mo—Ta alloy phase, rather than forming a piezoelectriclayer formed of AlN on the pure Mo phase.

According to an embodiment in the present disclosure, a leakage currentof a resonator may be reduced by manufacturing an electrode using aMo—Ta alloy.

In addition, in the case of Embodiment of Table 2, a squared value Kt²of an effective electromechanical coupling coefficient is measured as6.44, and in the case of Comparative example, a squared value Kt² of aneffective electromechanical coupling coefficient is measured as 5.93.

According to an embodiment in the present disclosure, the squared valueKt² of an effective electromechanical coupling coefficient may beimproved by manufacturing an electrode using a Mo—Ta alloy.

FIGS. 7 and 8 are schematic circuit diagrams of filters according toembodiments.

Each of a plurality of bulk acoustic wave resonators employed in thefilters of FIGS. 7 and 8 corresponds to the bulk acoustic wave resonatorillustrated in FIG. 1.

Referring to FIG. 7, a filter 1000 according to an embodiment is formedin a ladder type filter structure. In detail, the filter 1000 mayinclude a plurality of bulk acoustic wave resonators 1100 and 1200.

A first bulk acoustic wave resonator 1100 is connected between a signalinput terminal to which an input signal RFin is input and a signaloutput terminal from which an output signal RFout is output in series,and a second bulk acoustic wave resonator 1200 is connected between thesignal output terminal and a ground.

Referring to FIG. 8, a filter 2000 according to an embodiment is formedin a lattice-type filter structure. In detail, the filter 2000 includesa plurality of bulk acoustic wave resonators 2100, 2200, 2300, and 2400to filter balanced input signals RFin+ and RFin− and output balancedoutput signals RFout+ and RFout−.

As set forth above, according to embodiments in the present disclosure,a bulk acoustic wave resonator may secure reliability by preventingoxidation of electrodes.

In addition, robust characteristics may be secured from an etchingmaterial used in a process of manufacturing a bulk acoustic waveresonator.

While embodiments have been shown and described above, it will beapparent to those skilled in the art that modifications and variationscould be made without departing from the scope of the present inventionas defined by the appended claims.

What is claimed is:
 1. A bulk acoustic wave resonator comprising: asubstrate; a first electrode and a second electrode disposed on thesubstrate; and a piezoelectric layer disposed between the firstelectrode and the second electrode, wherein at least one of the firstelectrode and the second electrode includes an alloy of molybdenum andtantalum.
 2. The bulk acoustic wave resonator of claim 1, wherein thepiezoelectric layer comprises aluminum nitride.
 3. The bulk acousticwave resonator of claim 1, wherein a content of the tantalum (Ta) is 0.1to 50 atm %.
 4. The bulk acoustic wave resonator of claim 1, wherein acontent of the tantalum (Ta) is 0.1 to 30 atm %.
 5. The bulk acousticwave resonator of claim 1, further comprising an air cavity disposedbetween the substrate and the first electrode, wherein a sacrificial aircavity layer pattern for formation of the air cavity is etched by xenonfluoride.
 6. The bulk acoustic wave resonator of claim 5, wherein thesacrificial air cavity layer pattern is etched after at least one of thefirst electrode and the second electrode is formed.
 7. A filtercomprising: a plurality of bulk acoustic wave resonators, wherein eachof the plurality of bulk acoustic wave resonators includes: a substrate;a first electrode and a second electrode disposed on the substrate; anda piezoelectric layer disposed between the first electrode and thesecond electrode, and at least one of the first electrode and the secondelectrode includes an alloy of molybdenum and tantalum.
 8. The filter ofclaim 7, wherein the piezoelectric layer comprises aluminum nitride. 9.The filter of claim 7, wherein a content of the tantalum (Ta) is 0.1 to50 atm %.
 10. The filter of claim 7, wherein a content of the tantalum(Ta) is 0.1 to 30 atm %.
 11. The filter of claim 7, wherein each of theplurality of bulk acoustic wave resonators further comprises an aircavity disposed between the substrate and the first electrode, wherein asacrificial air cavity layer pattern for formation of the air cavity isetched by xenon fluoride.
 12. The filter of claim 11, wherein thesacrificial air cavity layer pattern is etched after at least one of thefirst electrode and the second electrode is formed.
 13. The filter ofclaim 7, wherein the plurality of bulk acoustic wave resonators areconfigured in at least one of a ladder type and a lattice type.